This invention relates to hovercraft and, more particularly, to ground-effect flying machines.
Hovercraft of various types have been known for a number of years and have been used to accomplish a variety of tasks. Some of these craft are of the helicopter type in which the down draft of rotating blades and the passage of air over the blades themselves, produce a vertical lift. Another type of hovercraft has a circular air foil wing with rotating blades mounted in a central cavity of the wing. The rotating blades draw air over the air foil surface and into the central cavity to produce the vertical lift for the craft. Craft of this type are disclosed in U.S. Pat. No. 2,876,964 to Streib, U.S. Pat. No. 2,936,972 to Zinavage, and U.S. Pat. No. 3,432,120 to Guerrero. In the Guerrero patent, additional lift is is also produced by the "ground-effect" which characterizes another type of vehicle.
Ground-effect vehicles or craft have a propeller or other air source which creates a cushion of air under the body of the craft, upon which it floats. This cushion of air is prevented from being dissipated by a skirt configuration that extends down from the body of the craft to a point close to the ground. Typical of such a vehicle is the cushion craft built by Britten Norman Ltd. of England.
Hovercraft in general can be used for a variety of purposes from toys to the transportion of passengers and cargo. One potentially useful application is in the spraying of crops with seeds, fertilizers, insecticides, etc. While this task can be accomplished by low-flying conventional aircraft, the effects of wind and the inability to accurately control the flight path, cause the spray to be wasted. This spray method may even cause environmental hazards by allowing insecticides to spread into residential areas adjacent the crops. Further, telephone poles and other tall structures makes this activity hazardous to the pilot.
Because of the short-comings and the relatively high cost of spraying by conventional aircraft, a good deal of crop spraying is accomplished by means of wheeled vehicles. This method is quite straightforward and simple; but its application is restricted to periods of time during which the ground is hard enough to carry a wheeled vehicle. Frequently in the Spring rainfall is quite heavy, soaking the ground and making it too muddy to support a vehicle. Thus, the farmer has to wait for favorable weather to dry the ground before he can bring his wheeled vehicle out to do this agricultural work. This waiting period will occasionally cause the farmer to miss the most favorable time for such activities, allowing crop pests to attack the young plants and causing his agricultural work to be out of phase with the most favorable seasonal weather conditions. Thus it can be seen that a tremendous loss of agricultural productivity to the country and loss of income to the farmers can occur, particularly to small farmers with limited resources.
It has been proposed to overcome this problem by carrying out such activities as seeding, crop dusting, spraying, etc., by means of hovercraft, such as helicopters. These vehicles operate at a distance above the ground so that they can be used without regard to the condition of the ground, i.e. whether or not it is muddy. Helicopters, however, are expensive to operate and still present a hazard to the pilot when used close to the ground. As an alternative the Gunderson Agricultural ACV, which is a manned, ground-effect machine, has been proposed for experimental crop spraying. See Cagle, Flying Ships, Hovercraft and Hydrofoils, Dodd Mead & Co. (1970). However, the principal problem with the use of either of these types of hovercraft for agricultural purposes is that they create a large down draft that can destroy young plants.